A technology is known that a GPS receiver uses multiple hardware correlating units to thereby increase a speed in synchronous acquisition for the GPS satellites. In such a GPS receiver using the multiple (or multiple-channel) hardware correlating units, a time period required for the synchronous acquisition decreases as the number of hardware correlating units increases. However, in the GPS receiver that includes hundreds or thousands of hardware correlating units so as to shorten the time period for the synchronous acquisition, a large number of hardware correlating units poses disadvantage such as increase in an LSI size, or manufacturing costs. Tracking the GPS satellites posterior to completing of the synchronous acquisition does not need as many as the hardware correlating units required for the synchronous acquisition. Therefore, the above large number of hardware correlating units is only needed for the synchronous acquisition that is mainly executed in starting powering.
To avoid this disadvantage and also achieve the high speed in the synchronous acquisition, a software correlating technology is proposed for use in a GPS receiver. In this technology, a certain amount of necessary signal data for the synchronous acquisition is obtained from the GPS satellites to then be stored in a memory, and the stored data is used by a CPU for a correlating process in a software manner (software correlating) so as to execute the synchronous acquisition and tracking.
Note that the synchronous acquisition that does not need to be repeatedly executed when it is executed once whereas the tracking is a real-time process so that repeated execution should be required at milliseconds of intervals. In the inventors' investigation, such high-frequency tracking is not easily achieved in the above software manner by a CPU of the present processing speed. If it is achieved, an excessively high performance CPU is required, so that manufacturing costs or a product size should be increased.